Astorino visited Rye and Mamaroneck on Monday morning and saw many residents, including children, still out on the streets even those those low-lying areas had already started to flood, he said in a news conference Monday.

“It’s very important right now that people start heeding the warnings,” Astorino said. “Stay inside. Do not go out and about.”

Mandatory evacuations have begun in Mamaroneck and Port Chester, although some residents chose not to leave. Astorino said those residents will have to live with that choice, because officials will not endanger officers unnecessarily.

“Those who have not evacuated, if there are problems later, we may not be able to get to you,” Astorino said. “So this is a perfect time still, with daylight … now is a time to please get out of the area if you can.”

Sustained winds and tidal surges began at about noon and high tide occurred about the same time in the Sound Shore and Hudson River areas.

Astorino listed low-lying Sound Shore communities such as Port Chester, Mamaroneck, Larchmont, Rye, Pelham and New Rochelle and low-lying Hudson River communities such as Dobbs Ferry and Irvington as the main areas of concern because they are most susceptible to flooding.

More mandatory evacuations are possible Monday afternoon, Astorino said, but he did not anticipate many more.

“What we don’t want to do is have mandatory evacuations in the middle of the storm,” he said.

If necessary, police and firefighters would go door-to-door to inform residents. Reverse 911 calls to cellphones and landlines could also be used, and any mass evacuations would be announced through the media and through Westchestergov.com.

Peak winds of up to 70 mph are forecast for 10 p.m. to midnight Monday and are likely to bring down trees and power lines. Scattered outages had already begun, but the county expected more outages as the storm progressed.

Con Edison and NYSEG will not be able to send workers out in bucket trucks to repair power lines with sustained winds blowing, Astorino said. The county executive urged residents to have patience and be prepared for the possibility of several days without power.

The power companies have already called in extra crews, some from out of state, and set up staging areas throughout the county so they can get to work as quickly as possible.

Live power lines that fall could also sit under water, so residents should avoid all power lines and water to avoid electrocution.

The National Guard is on standby in Westchester County, with 50 special vehicles with 100 drivers that can be called on as needed.

The county had plenty of time to prepare for Hurricane Sandy and began dealing with power companies as early as Friday, Astorino said. The county has not yet made any requests to FEMA.

Astorino addressed a small group of reporters at the Hudson Valley Transportation Management Center in Hawthorne. He recited a list of actions taken by the county and issued warnings to county residents, including:

• The Bronx River Parkway remains closed while other highways in the county remain open. Roads are subject to closure at any moment.

• The BeeLine and ParaTransit bus services will remain suspended likely through Tuesday, but they will resume running if the county can do so safely.

• The Westchester County Airport is open, but nearly all flights have been postponed. Travelers should check with individual airlines for flight statuses. Flights will likely resume Wednesday.

• Residents should dial 911 in case of emergency and 211 for non-emergency situations and to receive updates on the hurricane. Westchestergov.com will also have updates and shelter information.

• The water supply has not been disturbed, but turbidity levels could increase, which would lead to a boil water alert.